1. Field of the Invention
This invention relates to organic semiconductor devices and methods for making such devices.
2. Description of the Related Art
One potential area of application for organic field-effect transistors (OFETs) is in driver circuits of pixel displays. In such circuits, the desirable properties for OFETs include a high channel mobility, compatibility with making fine patterns of OFETs, and a high on/off drain-current ratio, the off drain-current being produced by a zero gate voltage. While several conventional OFETs have one of the above desirable properties, conventional methods have not combined all three properties in the same device.
For example, OFETs made from single pentacene crystals have high channel mobilities, e.g., 1-5 centimeter-squared per volt second (cm2/Vs) at room temperature. Unfortunately, these OFETs also have low on/off drain-current ratio, e.g., less than 105. Also, OFETs based on single pentacene crystals have not lead to the formation of fine device patterns even though the devices based on pentacene crystals can have short channel lengths, e.g., less than 10 microns.
As a second example, organic semiconductor thin films are compatible with forming fine patterns of physically separated semiconductor domains, e.g., linear inter-domain dimensions of 5 microns or less. These fine patterns enable construction of fine patterns of OFETs on a substrate. Unfortunately, the organic semiconductor thin films are typically polycrystalline, and thus do not produce high channel mobilities. Exemplary thin film OFETs have channel mobilities of less than 0.2 cm2/Vs at room temperature. As opposed to polycrystalline thin films, crystalline thin films of organic semiconductors are not generally available for producing OFET channels.